Spirogyra

Spirogyra is a genus of filamentous green alga of the order Zygnematales. It is commonly found in freshwater areas. Spirogyra is a photosynthetic, eukaryotic cell. Spirals of chloroplast surround the vacuole, within which the nucleus is supported by cytoplasmic strands.

In a remarkable example of conjugation, Spirogyra reproduces sexually by exchanging DNA between cells. Certain filaments in a loose parallel bundle of Spirogyra assume the female role, and others the male. The cells of adjacent filaments develop tubular extensions which grow towards one another and eventually fuse to form a continuous tube between the cells. Meanwhile the contents of each cell have formed a round sphere. The spheres from the male filament squeeze their way down the connecting tubes to fuse with a sphere of the female cell in the other filament. The result of this sexual union is the formation of a zygote (zygospore) within the chambers of the female filament. After a dormant period, the zygotes undergo meiosis and germinate, resulting in new filaments.